1. Field of the Invention
The invention relates generally to the field of oil and gas well operations devices. More specifically, the present invention relates to a method and apparatus to enhance safety when dislodging downhole tools from within a wellbore.
2. Description of Related Art
Certain procedures conducted in oil and gas producing wellbores are known as wireline operations. These operations typically involve attaching a wireline to a tool that lowers, supports, and raises the tool within the wellbore during wireline operations. In addition to the capability to raise and lower the tool within the wellbore, the wireline can also carry signals between the surface and the tool.
The path of a wellbore, while often containing long straight runs, can also include bends, elbows, or other discontinuities. On occasion, when the tool or wireline encounters these discontinuities, either the wireline or the tool can become wedged in the wellbore such that the force required to dislodged them exceeds the tensile strength of the wireline. To remove or dislodge the tool or wireline without breaking the wireline, the tool or wireline is often “fished” out of the wellbore. Fishing for downhole tools generally involves lowering a fishing tool into the wellbore on a string of pipe segments to the stuck tool or wireline. When the fishing tool encounters the stuck tool or wireline, it can be manipulated to grapple the stuck item and extract it from the wellbore.
To help guide the fishing tool to the stuck tool or wireline a cut and thread method is often used. Cut and thread operations involve severing the wireline above the surface (the top wireline 32) and attaching a wireline connection 28 to each severed end of the wireline. FIGS. 1a and 1b illustrate details of the fishing spear 10 and the fishing overshot 20 of the wireline connection 28. FIGS. 2a-2c depict certain aspects of a cut and thread operation. Typically a fishing spear 10 is attached to the portion of wireline that remains in the wellbore (bottom wireline 34) and a fishing overshot 20 is attached to top wireline 32. The fishing overshot 20, with attached wireline, is then threaded through a pipe segment 30 and mates with the fishing spear 10 on its upper end 26 to form a wireline connection 28. As the fishing spear 10 is inserted into the upper end 26 of the fishing overshot 20, the tip 14 of the fishing spear 10 contacts dogs 23 formed on the inside upward end of the latching fingers 22. The contact between the tip 14 and the dogs 23 pushes the upward end of the latching fingers 22 outward until the tip 14 travels past the dogs 23. The latching fingers 22 are spring loaded and will snap back into their original position after the tip 14 passes past the dogs. When the fishing spear 10 is fully inserted into the fishing overshot 20, the dogs 23 are proximate to the spear neck 15 and below the tip 14. The spring loaded latching fingers 22 maintain the dogs 23 in place behind the tip 14 and prevent the tip 14 from traveling past the dogs 23, this secures the fishing spear 10 to the fishing overshot 20.
After the wireline connection 28 is formed, the pipe segment 30 is then lowered into the wellbore, over the now connected fishing spear 10 and fishing overshot 20 until the wireline connection 28 emerges from the top of the pipe segment 30. When the wireline connection 28 is outside of the pipe segment 30, the fishing overshot 20 is disconnected from the fishing spear 10 by depressing the tab 21 on the latch fingers 22 and thus urging the dogs 23 out and away from the fishing neck 15. After the fishing overshot 20 is removed from the fishing spear 10 it can then be threaded through another pipe segment and the process repeated. The subsequent pipe segments 30 are attached to form a drill string that lengthens with each added pipe segment 30 until the fishing tool is in position to grapple and remove the stuck item.
Cut and thread fishing operations have always suffered a common hazard, as the drilling blocks/top drive 18 is lowered towards the drill floor 6, it deflects the top wireline 32 away from vertical. Deflecting the top wireline 32 from vertical causes the wireline connection 28 exiting the top of the pipe segment 30 to be suddenly exposed to a bending moment. In recent years the diameter of modern drilling top drives 18 has gradually increased, which in turn increases the deflection of the wireline 32 during fishing operations, which ultimately increases the bending moments exerted on the wireline connection 28.
As can be seen in FIG. 2c, this hardware arrangement, as well as many others, results in the top wireline 32 exiting the pipe segment 30 not exactly vertical, but instead at an angle from vertical. In situations when the top wireline 32 is not exactly vertical, the wireline connection 28 experiences a bending moment as it emerges from the pipe segment 30. This is a very dangerous situation if the applied bending moment exceeds the yield strength of the wireline connection 28. If the wireline connection 28 fractures during cut and thread operations, its respective pieces will most likely become airborne and are capable of causing serious bodily injury, including fatalities. Therefore, there exists a need for an apparatus and method to improve the safety of cut and thread wireline operations performed at a wellsite without hindering or slowing the cut and thread operations.